In a semiconductor laser, there is a Q-switch operation as a method of obtaining a high-power pulse by controlling oscillation. In the Q-switch operation, optical loss is initially increased to suppress oscillation, thereby facilitating optical pumping to cause the number of atoms in excited states to sufficiently increase; at that point in time, a Q-value is raised, thus allowing for oscillation. The semiconductor laser that allows for the Q-switch operation is described in the following PTLs 1 to 5, for example.